FIG. 1 shows the structure of the optical connector connecting structure disclosed in Japanese Patent Application Laid Open No. 2012-68323 (referred to hereinafter as Literature 1) as an example of such an optical connector connecting structure in the prior art. In Literature 1, the optical connector connecting structure includes a housing and an adapter. The housing 10 holds an optical connector 21, while the adapter 31 to be coupled to the housing 10 is secured to an enclosure 32 so as to cover a portion of the optical module 33 partially protruding outward from the enclosure 32.
The housing 10 has a cylindrical portion 11, an outer cylindrical portion 12, a connection member 13, and a cable 14 connected to the connection member 13. The connecting end of the cylindrical portion 11 serves as an engagement portion 11a. A support portion 11b is formed in the engagement portion 11a to support the optical connector 21 such that the optical connector 21 is movable in the axial direction. A through hole 11c is formed in the support portion 11b, into which an attachment member 22 attached to the optical connector 21 is inserted.
The optical connector 21 has main body portions 21a. The attachment member 22 is attached to the base end portions of the main body portions 21a. The attachment member 22 has a main body portion 22a, base end portions 22b, and a flange portion 22c. The main body portion 22a extends through the through hole 11c. Although not shown in FIG. 1, boots for protecting optical fiber cables 23 are secured to the main body portions 21a of the optical connector 21. The attachment member 22 is attached so as to cover the boots.
A partition 15 having a through hole 15a formed therein is secured to the cylindrical portion 11 on the base end side of the support portion 11b. Coiled springs 16 are provided between the partition 15 and the flange portion 22c of the attachment member 22. The base end portions 22b are inserted into the springs 16. Urging force of the springs 16 urges the attachment member 22 in the axial direction toward the connecting end. The optical connector 21 is thereby urged in the axial direction toward the connecting end.
The cylindrical portion 11 has a sliding portion 11d formed therein. The sliding portion 11d has the maximum outer diameter and is slidable with respect to the inner surface of the outer cylindrical portion 12, so the outer cylindrical portion 12 is rotatable with respect to the cylindrical portion 11 about the axis. The outer cylindrical portion 12 is movable with respect to the cylindrical portion 11 within a predetermined range in the axial direction. A ring member 17 made of rubber is provided in a recess of the cylindrical portion 11.
The connection member 13 is connected to the cylindrical portion 11 on the base end side thereof. A ring member 18 made of rubber is provided between the connection member 13 and the cylindrical portion 11. The cable 14 is connected to the connection member 13 on the base end side thereof. The optical fiber cables 23 from the optical connector 21 are inserted into the cable 14.
Ferrules 21b and springs 21c that urge the ferrules 21b in the axial direction toward the connecting end are held in the main body portions 21a of the optical connector 21. Latch arms 21d are provided on the main body portions 21a. The optical fiber cables 23 are connected to the main body portions 21a on the base end side thereof and the ferrules 21b are connected to the optical fibers inside the main body portions 21a. 
The adapter 31 is engaged with a hole portion formed in the enclosure 32. The adapter 31 has an engagement portion 31a that engages with the cylindrical portion 11. An annular engagement groove portion 31b is formed in the engagement portion 31a on the base end side thereof. The engagement groove portion 31b is continuous with the inner surface of the engagement portion 31a. A through hole 31c is formed in the adapter 31. The connecting end of the optical module 33 inserted through the through hole 31c protrudes from the through hole 31c. A ring member 34 made of rubber is provided between the base portion 31d of the adapter 31 and the enclosure 32.
The optical module 33 has insertion holes 33a into which the optical connector 21 is inserted. Ferrules 33b to be connected to the ferrules 21b in the optical connector 21 are provided within the insertion holes 33a. The ferrules 33b are urged by springs 33c in the axial direction toward the connecting end.
In such a configuration, when the adapter 31 and the housing 10 are coupled to each other, the engagement portion 31a of the adapter 31 is inserted between the outer cylindrical portion 12 and the cylindrical portion 11 of the housing 10 and the engagement portion 11a of the cylindrical portion 11 is inserted into the engagement groove portion 31b. The ferrules 21b and 33b are brought into press contact with each other and the optical connector 21 moves in the axial direction toward the base end against the urging force of the springs 16.
The optical connector 21 is thus supported movably in the axial direction. When the optical connector 21 is connected to the optical module 33, variations in the length of the optical module 33 in the axial direction that differ with the type of the optical module 33 are accommodated and the optical connector 21 can be connected to the optical module 33.
As described above, in Literature 1, the optical connector 21 held in the housing 10 is movable with respect to the cylindrical portion 11 in response to the position of the connecting end of the optical module 33 (i.e., length of the optical module 33) in the adapter 31. On the other hand, the optical fiber cables 23 connected to the optical connector 21 are fixedly secured to the connection member 13 on the base end side of the cylindrical portion 11. When the optical connector 21 moves in the axial direction toward the base end, the optical fiber cables 23 would bend.
Since the optical fibers are made of glass and are vulnerable to bending (fragile when bent), it is necessary to provide an extra length to each optical fiber that is long enough to prevent the radius of curvature of the optical fiber from becoming small when the optical fiber is bent.
It is necessary, therefore, that the cylindrical portion 11 in Literature 1 admits such an extra length for the optical fiber. Hence, there are drawbacks that the cylindrical portion 11 cannot be shortened and therefore the housing 10 cannot be reduced in size.